Means for operating electric eddy current furnaces



March 2, 1937. L, DREYFUS 2,072,549

y MEANSAFOR OPERATING ELECTRIC EDDY CURRENT FURNCES Filed Nov. 2e, 1935 Patented 2, 1937 MEANS FOB OPERATING ELECTRIC EDDY CURRENT FUBNACES Ludwig Dreyfus, Vasteras, Sweden, asslgnor to Allminna Svenska Elektriska Aktiebolaget,'

` Vasteras, Sweden, a corporation of Sweden Application November 26, 1935, Serial No. 51,589

In Sweden September 20, 1934 Y 7Claims.

I have filed an application in Sweden September 20th, 1934.

'I'his invention relates to installations of electric eddy current furnaces.

It has been heretofore proposed to provide such installations in which the winding is divided into several sections connected in series and it has also been proposed to divide the current source feeding the said.winding into several sec- 10 tions connected between the sections of the furnace winding, and condensers for compensating the reactance of the furnace winding sections are connected with the latter lin parallel or in series.

It is found in practice that the said reactance is strongly variable, not only during the vsame melting process, depending on the difference in the electric and magnetic properties of the solid and the molten metal, but also for different melting processes, depending on the different degree of filling ofthe furnace. It is always desirable that the compensation of the reactance be as accurate as possible, and this necessitates an adjustment of the capacity of the condensers.

It has now been found that, for an alternating series connection of sections of the current source and of the furnace winding, the said adjustment can be essentially simplied if the condensers, instead of being connected in'series or in parallel to the furnace winding sections, are connected between the terminals of the current source sections. Such a connection forms the object of the present invention. An examination shows that by such a connection all the condensers belonging to a number of series connected furnace Winding sections can be adjusted in common for being adapted to the total reactance, of the winding sections, said total reactance as a rule, being not subjected to proportional variations so large as the separate partial' reactances. 'Ihis is the case particularly if the different winding sections, are situated at different height because the reactance then increases` for an upper section .at the same time as it decreases for a lower one by reason of the flowing-down of the molten metal from the Y former section to the latter.

The reason for connecting sections of the fur*-` different species Yof current and to reduce the mutual action of these on-each other to the smallmay then for-- instance belong' to different phases of the low frequency system.

Three forms of the invention arranged in last-mentioned way are atically shown l0 in the accompanying drawing in Figs. 14%. For simplifying the different diagrams 'of connection, different parts of such windings which generally are mounted on the same machine, are

placed in the diagram distant from each other l5v and close to the portions of the furnace winding with which they cooperate most closely.

In Fig. l, the furnace winding is connected in twophase for the low frequency stirrlng current and is for this purpose divided into four 20 sections or coils U1, Ua, Us, U4, which are supposed to be mounted above each other in the order mentioned, for instance with U1 at the top. For the high frequency current, the coils are series-connected in pairs, U1 being connected z5 in series with U4, and Us being connected in series with U2. In operating the furnace, the top coil will frequently obtain the highest reactance and the bottom coil the lowest reactance, because the former may often be practically without any 30 secondary circuit (when the furnace is not completely filled) while the latteris very soon lled with a completely molten charge, which therei fore reaches the wall of the furnace crucible. By'

' nected in parallel to the said generator winding sections. Those of the latter sections which feed `the circuit containing U1 and U4, are designated by H1 and H4 and those belonging to the other circuit by Hz and H3. The generator windings are series-connected with condensers for compen'satingV their inherent reactances, said con- 50 densers being individual for the generators Hz and H4. and designated by Sz and S4, but for the windings H1 and Ha combined into a common condenser S13. It is also possible to combine the windings H1 and Ha. into one. In this manner, 55

each combination of a winding and a series condenser will at its terminals thus give a practically constant voltage independent of the load. In parallel to each such combination, there is connected a condenser, C1, Cz, Ca, C4 respectively, for compensating the reactances of the furnace windings. Finally, a pair of windings L13 and L24 of a low frequency twophase generator are so connected that the former winding will feed the coils U1 and U3 in series while the latter feeds the coils U4 and U2 in series. If the windings are so wound that the high frequency ampere turns will reinforce the fluxes of each other, the low frequency ampere turns will then counteract each other in the axial direction, but instead of that cooperate in such a manner as to form a substantially radial flux wandering in a vertical direction, said ilux producing, in cooperation with the eddy currents induced thereby in the furnace charge, vertical tangential forces for stirring the charge. I'his dierent action of the high frequency and of the low frequency ampere turns is indicated in the figure by full-drawn arrows for the former on'es and dotted arrows for the vlatter ones. The same arrows also represent the directions of current in the coils so as to make it possible to check the course of the different currents.- The condensers form bars to the low frequency currents, and the windings of the low frequency generator bar the high frequency currents when the distribution of inductance is uneven, while on the other hand no such barring is necessary when the inductance distribution is e'ven, because the points connected through the low frequency windings are then equipotential points for -the high frequency current.

Figs. 2 and 3 show two .different examples of the connection for a threephase arrangement of the low frequency circuits. In both cases, the furnace winding and the windings of the high frequency and low frequency generators are divided into six sections or coils each.l In Fig. 2, the furnace coils are connected in pairs alternately with the main condensers so as to form three circuits. The first circuit, for instance,

.contains the top coil U1 `and the bottom coil Us of the furnace and the corresponding condensers C1 and Cs'in parallel to the high frequency generator windings H1 and H11 with their series condensers S1 and Se. The second circuit contains the furnace coils Us and U4 and the condensers Cs and C4 and the high frequency generator windings H5 and H4 with their series condensers S5 and S4. The third circuit contains the furnace coils Us and Uz, the condensers Cs. vand Cz and the high frequency Ygenerator windings Ha and Hz with their series condensers S3 and Sz. Between the angles of the three high frequency circuits, the windings L11- Lc ofthe low frequency generator are connected in such a .manner that a current phase generated by L1 two closed circuits, each containing three coils of each kind. One of the circuits contains the coils having odd numbers and the other the coils havingeven numbers. Otherwise the confurnace winding sections, and condensers for compensating the reactance of said furnace winding connected between the terminals of said current source sections.

2. In electric eddy current furnace installations.

,M a furnace winding divided into sections combined into independently fed groups, a high frequency current source for feeding said furnace winding divided in a corresponding mannerinto groups of sections, the individual current source sections in each group being each separately connected in series with a different individual section of the furnace winding in each group, and condensers for compensating the reactance of said furnace Q winding connected between the terminals off said current source sections. 3. In electric eddy current furna installations. a crucible, a winding surrounding said crucible and divided into sections arranged one above the other, a high frequency current source divided into sections individually connected in series with said furnace winding sections, and condensers for compensating the reactance of said furnace winding connected between the terminals of said current source sections.

4. In electric eddy current furnace installations.

`a crucible, a winding surrounding said crucible and divided into sections which are arranged one above the other and combined into independently fed groups, sections mounted at considerable distance from each other being combined into one group, a high frequency current source for feeding said furnace winding divided in a corresponding manner into groups of sections, the current source sections in each group, being connected alternatingly in series with the furnace winding sections in each group, and condensers for compensating the reactance of said furnace winding connected between the terminals of said cin-rent source sections.

5. In. eddy current furnace installations, a furnace winding divided into sections, a high frequency current source divided into sections connected alternatingly in series with said furnace winding sections, condensers Vfor compensating the reactance of said furnace winding connected between the terminals of said current v source sections, and a twoor polyphaselow frequency current source connected to feed each phase of current through at least two furnace winding sections, half of the number of these in opposite direction to the others, compared with the direction of the high frequency current.

6. In electric eddy current furnace installations, a furnace winding divided into sections combined into independently fed groups, a high frequency current source for feeding said furnace winding divided in a corresponding manner into groups of sections, the current source sections in each group being connected alternatingly in series with the furnace winding sections in each group, condensers for compensating the reactance of said furnace winding connected between the terminals `of said current source sections, and a multiphsse low frequency current source connected to feed each phase of current through at least two furnace winding` sections .belonging to different groups. Y

'1. In electric edilyl current furnace installations, a furnace winding divided into sections combined into independently fed groups, a high frequency current source for feeding said furnace winding divided in a corresponding manner into groups of sections. the current source sections in each group being connected alternatingly in series with the furnace winding sections in each group. condensers for compensating the reactance of said furnace winding connected between the terminals of said current source sections, and a multiphase low frequency current source having each phase divided into several series-connected portions which are connected between different points of said groups of the furnace winding and of the high frequency current source.

LUDWIG DREYFU 

